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-   -   simulate the drying process (http://www.cfd-online.com/Forums/fluent/89356-simulate-drying-process.html)

Valpress June 10, 2011 05:00

simulate the drying process
 
Hello everyone,

I would like to ask a question corcerning a posibility to simulate drying process of a fiber material (i.e cotton towel). I am doing my PhD. and investigate this possibility in ANSYS Fluent 13.0

At the present I set the simulation this way:

1. geometry - there is a pipe and porous volume inside. Hot air (mass flow) is defined at the inlet. Porous volume should have represented i.e. cotton towel.
2. I used Multiphase-Eulerian model, 3 phases (air, water, vapor); there is mass transfer-evaporation set in phases interaction dialog box. It looks that evaporation works quite well.
3. water is PATCHed in porous volume cell zone as volume fraction after initialization

By this steps i would want simulate drying but I am not sure whether I can use porous volume (porous zone) for this. Problem occures when hot air is passing through porous zone - than the water escapes this porous zone after short time (circa 0.8 sec). Simulation is set as transient (time step 0,001sec). Porous coeficients was set the way reflecting real test (pressure drop in the pipe).

Has anybode some information about possibilities to simulate this case. i think that main goal is find out how to "hold" water phase in porous zone longer time and evaporate it- means do not allow to escape it immediately with passing air.

Unfortunatelly I can not use Ansys customer portal to ask the experts because our university doesnīt have maintenance.

Thanks a lot for any information.

Cantstandit June 20, 2011 07:48

you could use "fixed value" option in the cell zone conditions, and set the liquid water phase velocity components to 0, this way it will always stay in the porous zone.

Valpress June 23, 2011 05:39

Dear Cantstandit,

thank you very much for your advice. I should invite you for beer. This "fixed values" seems to be helping. For at the first sight it looks that I am simulating drying of a fiber (which is representing by porous zone) in Fluent.

Thanks, thanks, thanks :)

jacek May 10, 2013 04:41

I did the same as said:
 
1. Geometry - simple pipe, part of it as porous, water inside,
2. Mulitphase Eulerain model, air, water-liquid, water-vapour,
3. Water is patched in porous volume after initizlization
4. Liquid water is fixed in porous volume U=V=Y=o m/s to prevent it from hovering with air

but when calculation is started I got error:

# Divergence detected in AMG solver: pressure correction -> Turning off correction scaling!
# Divergence detected in AMG solver: k -> Increasing relaxation sweeps!

Error: Divergence detected in AMG solver: k
Error Object: #f

Interrupting...
Done.

What is the problem with divergence?

niloogh May 23, 2013 19:27

Quote:

Originally Posted by jacek (Post 426482)
1. Geometry - simple pipe, part of it as porous, water inside,
2. Mulitphase Eulerain model, air, water-liquid, water-vapour,
3. Water is patched in porous volume after initizlization
4. Liquid water is fixed in porous volume U=V=Y=o m/s to prevent it from hovering with air

but when calculation is started I got error:

# Divergence detected in AMG solver: pressure correction -> Turning off correction scaling!
# Divergence detected in AMG solver: k -> Increasing relaxation sweeps!

Error: Divergence detected in AMG solver: k
Error Object: #f

Interrupting...
Done.

What is the problem with divergence?

hi jacek
i have a problem such as you.(Error: divergence detected in AMG solver)
did you solve your problem?
if it,s possible for you help me in this case:(

jacek May 24, 2013 05:05

My problems with divergence stopped when I remove boundary layers from the pipe.
But more a important thing was setting a correct temperature of boiling in normal conditions - 380 K, slightly over boiling point. Then there were no problems with convergence when boiling really runs.

But this gave me suspicion if one has to to with boiling or evaporation in Fluent.
If it should be evaporation of water to surrounding air, evaporation take place in every given temperature. But there must be saturation point - max water vapour partial pressure of vapour in given temperature in humid air (relative saturation = 100%).

For now I can't see saturation in Fluent, however this temperature is in phases mass interaction so named. If it were evaporation Fluent would have saturation curve P-t and humid air balance implemented.

niloogh May 24, 2013 05:27

Quote:

Originally Posted by jacek (Post 429720)
My problems with divergence stopped when I remove boundary layers from the pipe.
But more a important thing was setting a correct temperature of boiling in normal conditions - 380 K, slightly over boiling point. Then there were no problems with convergence when boiling really runs.

But this gave me suspicion if one has to to with boiling or evaporation in Fluent.
If it should be evaporation of water to surrounding air, evaporation take place in every given temperature. But there must be saturation point - max water vapour partial pressure of vapour in given temperature in humid air (relative saturation = 100%).

For now I can't see saturation in Fluent, however this temperature is in phases mass interaction so named. If it were evaporation Fluent would have saturation curve P-t and humid air balance implemented.

tnx jacek
i think my problem is related to my periodic bcs.
and still i didn,t fix it:(


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